Raffinate Solution Heater For Compania Minera Cerro Colorado Copper Mine Iquique, Chile

PROJECT OVERVIEW

Case study - Compañía Minera Cerro Colorado (Raffinate Solution Heater CMCC in Spanish) 

In 1995, Inproheat supplied a 10 MM BTU/hr raffinate (acidic copper-barren solution from the solvent extraction process) heating system for the Compania Minera Cerro Colorado (CMCC) copper mine in Iquique, Chile. This large copper mine is situated in a remote location at 2,500 metres above sea level. A two hour drive east from Iquique takes a visitor deep into the mountainous barren landscape. Long conveyors transport ore into the primary and secondary crushers. Crushed ore is then sent to an agglomerator where marble-size to golf-ball-size ore nodules are formed. Nodules are conveyed to heap leaching pads where they are stacked 50 feet high. Raffinate is constantly pumped to the heaps through a piping system. As it trickles through the ore heap it leaches copper and other minerals from the ore nodules. Pregnant leach solution is then collected at the bottom of the pads and pumped to the solvent extraction (SX) plant for copper recovery. The copper is then converted to metal in the electrowinning process plant.
Before the SX raffinate is recirculated to the heap pads, it is heated from 15 to 35° C to improve the kinetics of leaching process. The primary source of energy for the mine is the No.2 diesel fuel. Propane is available in limited quantities.

Raffinate CMCC-83

THE CHALLENGE

Raffinate is a mild solution of sulphuric acid with a pH between 1.2 and 2.0. An investigation of proper materials of construction for the system was required, both for the combustion chamber, solution tank and piping and valves.

  • Inproheat's experience with existing installations was limited to gaseous fuels. The utilization of No.2 diesel fuel oil had to be researched.
  • The location of the site at 2,500 meters (8,250 ft) A.S.L. elevation had to be taken under consideration when designing the combustion system components.

The unit was to be mounted outdoors and capable of automatic operation with remote start/stop from the control room.  The requirement for high efficiency is dictated not only by economics but also by logistics of trucking diesel fuel to a remote mine location high in the mountains.

THE SOLUTION

Inproheat designed and manufactured a 10 MM BTU/hr SubCom® submerged combustion system for raffinate heating. Metallurgical tests were undertaken to establish the best material for the combustion chamber. Carpenter 20Cb-3 alloy was selected for all combustion chamber components.
The tank, vent stack and piping were made of fiberglass using an acid resistant Derakane 411-45 resin.

To handle corrosive raffinate Inproheat selected Durco valves and a pump made of CD4MCu alloy.
Propane was used as a fuel to burner pilot and #2 diesel oil as the main fuel.

The unit was skid-mounted, prepackag ed and prewired including the heating tank, SubCom® burner, combustion air blower, propane pilot fuel train, diesel oil main train, inlet water shutoff and control valve, discharge pump, and control panel. The fiberglass vent stack was shipped separately. CMCC provided the raffinate inlet and outlet connection and fuel supply. Raffinate is fed by gravity from a large storage tank adjacent to the heating system. An inlet control valve maintains the water level inside the heater. On the discharge side, a centrifugal pump removes heated raffinate from the SubCom® tank.

THE RESULT

To address the technical uncertainties of the project, Inproheat decided to simulate system operation with water at the factory. The system was tested for approximately 2 weeks. A 50 Hz generator was rented to match the frequency of power supply in Chile. A cold water supply of approximately 130 USGPM was connected to the heater, and high altitude operation of the blower was simulated by restricting the inlet to the combustion air blower.

Initially a problem was developed with self-generation of waves in a round-domed fiberglass tank. This problem was quickly resolved by addition of wave attenuating baffles inside the tank.

Performance of the diesel fuel burner exceeded expectations. Initial concerns of potential oil residue in the raffinate were alleviated by water discharge quality tests. All system functions and performance were tested before shipment to Chile.

Inproheat commissioned and started the system up in November 1995. A number of combustion tests were conducted. The raffinate discharge temperature was set at 35°C, with stack temperature between 34 and 36°C. The resulting overall system efficiency was calculated at 93% of the diesel oil higher heating value, with US$12/hr savings compared to a conventional boiler / heat exchanger system.

The successful system operation resulted in a repeat order. A second identical SubCom™ raffinate heater was installed at CMCC and commissioned in July 1996.